Previously, --verify would work even if the sources were built with
default options. However, in the interests of performance, --verify is
now only available if --enable-debug was passed to configure.
double has been disabled, because I am no longer packaging the gdtoa library
with Ledger (because double conversion really has nothing to do with what
Ledger does). If you wish to use it, you can find gdtoa in cpp-rewrite-2006,
under a sub-directory of the same name.